If you want a kind of Advance mode simply open a Terminal.
To do this go to Files > My Documents to open the File Manager. Then go to File > Terminal.
The Linpus Linus is using Xfce, so use
xfce-setting-show
to get the Xfce Settings Manager.
Click on Desktop to get to the Desktop Preferencs and choose the Behavior tab.
Now mark under Menus the Show desktop menu on right click option and close the window.
This setting will allow you to bring up the normal desktop menu when you right click somewhere on the desktop. The Desktop Menu contains much more options than the limited user interface on the Aspire One.
Unter System you will find Add/Remove Software which is the Red Hat/Fedora Packet Manager. You will need your password (the one you set up during installation) to access it. Now you can go nuts and install programs. It's a pretty big selection and the files will be downloaded (you need internet access) and installed for you. If it's an application you usually find it later in the Desktop Menu.
That should be enough for the average user. The advanced ones will just use the Terminal to access what they want.